The established processes for the extraction of uranium from ore are sulphuric acid and sodium carbonate leach processes and in a few limited instances, in situ and pressure leaches using ammonium carbonate. The standard recovery of uranium in most of these processes is achieved through the processing of the uranium leachate using ion and solvent extraction to produce ammonium di-uranate (ADU), followed by a calcining process for the production of pure (above 95%) yellow cake (uranium oxide mixture)
The extraction of uranium from ore using ammonium carbonate as a leach reagent has been proposed in U.S. Pat. No. 4,405,567 (Stapp), but this process did not find industrial acceptance because the technologies to apply it efficiently on an industrial basis were not available.
The known processes for the recovery of uranium that could be applied to an ammonium carbonate pregnant solution include steam stripping, ion exchange and solvent exchange, but none of these processes, alone or in combination, can provide the desired efficiency in recovering uranium.
A method for the removal of uranium from an aqueous phosphoric acid solution is also described in U.S. Pat. No. 4,206,049 (Stana et al), which comprises passing the uranium containing solution through a reverse osmosis membrane to concentrate the uranium and then concentrating the uranium further by flushing it with water and passing it through a further reverse osmosis membrane. This method has not been accepted for the industrial recovery of uranium from leached solutions, primarily because of inefficiencies in the process and not allowing for the recovery of unused reagents.
The present invention seeks to provide for industrial extraction of uranium that is energy and capital efficient, that allows for the recovery of a high percentage of water and leach reagents, and which provides for the efficient precipitation of uranium with a high degree of purity.
The invention furthermore seeks to achieve precipitation of uranium at a high degree of efficiency and purity, attaining this by minimising the use of the ion exchange process and eliminating the generally accepted solvent extraction process.